Method for recycling polyester fabrics with use of ionic liquid catalyst

Abstract

A method for recycling polyester fabrics with use of an ionic liquid catalyst is provided, which includes: providing a recycled polyester fabric; and using a chemical de-polymerization liquid to chemically de-polymerize the recycled polyester fabric and form a de-polymerization product that includes bis-2-hydroxylethyl terephthalate (BHET). The chemical de-polymerization liquid is used to chemically de-polymerize the recycled polyester fabric in an environment where a de-polymerization catalyst exists, and the de-polymerization catalyst is the ionic liquid catalyst in a solid state.

What is claimed is: 
     
         1 . A method for recycling polyester fabrics with use of an ionic liquid catalyst, comprising:
 implementing a preparation operation, which includes providing a recycled polyester fabric;   implementing a de-polymerization operation, which includes using a chemical de-polymerization liquid to chemically de-polymerize the recycled polyester fabric and form a de-polymerization product, wherein the de-polymerization product includes bis-2-hydroxylethyl terephthalate (BHET); wherein the de-polymerization operation is to chemically de-polymerize the recycled polyester fabric in an environment where the ionic liquid catalyst is present; wherein the ionic liquid catalyst includes a substrate and ionic liquids grafted onto the substrate, the substrate is made of carbon, silicon, iron, nickel, and/or cobalt, and an average particle size of the substrate is between 2 micrometers and 800 micrometers; and   implementing a separation operation, which includes separating the ionic liquid catalyst from the de-polymerization product by one or both of a centrifugal method and a filtering method, so as to collect and recycle the ionic liquid catalyst for use.   
     
     
         2 . The method according to  claim 1 , wherein, in the de-polymerization operation, the chemical de-polymerization liquid is ethylene glycol (EG), and the chemical de-polymerization liquid is heated to a de-polymerization temperature between 180° C. and 260° C., so as to chemically de-polymerize the recycled polyester fabric. 
     
     
         3 . The method according to  claim 1 , wherein, in the ionic liquid catalyst, the ionic liquids are at least one material selected from a group consisting of 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), 1-butyl-3-methylimidazolium tetrachlorozincate (BMI 2 ZnCl 4 ), 1-butyl-3-methylimidazolium tetrachloroironate (BMI 2 FeCl 4 ), 1-butyl-3-methylimidazolium tetrachlorocobaltate (BMI 2 CoCl 4 ), and 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF 4 ). 
     
     
         4 . The method according to  claim 1 , wherein, in the ionic liquid catalyst, a bridging agent for grafting the ionic liquids onto the substrate is a silane coupling agent; wherein a preparation method is to acidly de-compose the silane coupling agent before the silane coupling agent carries out a grafting reaction with the substrate, and to graft the ionic liquids onto the silane coupling agent in an alkaline environment, so as to form the ionic liquid catalyst. 
     
     
         5 . The method according to  claim 1 , wherein, in the separation operation, the ionic liquid catalyst has a higher specific gravity relative to the de-polymerization product, so that the ionic liquid catalyst is capable of being separated from the de-polymerization product through sedimentation; wherein a catalyst recovery rate of the ionic liquid catalyst is not less than 95%. 
     
     
         6 . The method according to  claim 1 , wherein, after the separation operation, the method further includes implementing a purification operation to obtain purified bis-2-hydroxyethyl terephthalate from the depolymerization product, wherein the purification operation includes an adsorption process; wherein the adsorption process includes: dissolving the bis-2-hydroxylethyl terephthalate into water to form an aqueous phase liquid, and adding one or both of an activated carbon material and an ion exchange resin into the aqueous phase liquid, so that one or both of the activated carbon material and the ion exchange resin absorb impurities originally present in the recycled polyester fabric. 
     
     
         7 . The method according to  claim 6 , wherein the aqueous phase liquid is heated to a liquid temperature between 70° C. and 150° C., so as to increase solubility of the bis-2-hydroxylethyl terephthalate in the water and to enable one or both of the activated carbon material and the ion exchange resin to adsorb the impurities under the liquid temperature. 
     
     
         8 . The method according to  claim 7 , wherein, after the adsorption process, the purification operation further includes a crystallization process; wherein the crystallization process includes: cooling the aqueous phase liquid from the liquid temperature between 70° C. and 150° C. to a crystallization temperature between 5° C. and 25° C., so that the bis-2-hydroxylethyl terephthalate is crystallized out from the aqueous phase liquid, and the purified bis-2-hydroxylethyl terephthalate is obtained.